1. Field of the Invention:
This invention relates to cold formed, sheet metal, profiled building units such as those useful as floor, wall or roof elements or other structural elements, and more particularly to improvements in such profiled building units and method for making the same.
2. Description of the Prior Art:
Roll formed sheet metal decking units currently present integral embossments, indents and formed ribs that interlock with a layer of concrete poured thereover to provide a composite floor slab. Such sheet metal decking units have been produced for more than twenty-five years and have been used in hundreds of millions of square feet of composite floor slabs.
Such decking units typically present flat regions, such as, alternating crests and valleys and sloped webs connecting adjacent ones of the crests and valleys. Since the sheet metal used to produce the decking unit has a substantially uniform thickness and since the decking units are roll formed, the crests, the valleys, the webs and the longitundinal stiffening ribs also are essentially of substantially the same uniform thickness with some minor localized stretching occurring at the outer periphery of the radii portions and minor localized compressing occuring at the inner periphery of the radii portions. In current roll forming practice, the smaller individual intermittent indents and embossments of composite decking units are stretched-in.
One of the earliest roll formed decking units exhibiting composite characteristics, utilized only embossments or their equivilents in the webs, see SHEA U.S. Pat. No. 3,397,497.
A later roll formed composite decking unit utilized longitundinal ribs in the crests and in the webs as well as embossments in the webs and in the valleys to provide a decking unit having improved "wet strength" and "composite characteristics" superior to those of the SHEA '497 decking unit, see for example ALBRECHT et al. U.S. Pat. No. 3,812,636. Other recent examples of such roll formed composite sheet metal decking units will be found in WASS U.S. Pat No. 4,144,369; TING U.S. Pat. No. 4,453,364; and STOHS U.S. Pat. No. 4,726,159.
Other building units having flat regions requiring stiffening against buckling, include corrugated roof deck, and wall structure elements such as profiled facing sheets and liner sheets. The prior art is replete with examples of such building units.
Currently the building units, such as, facing sheets, liner sheets, and decking units; and individual structural elements, such as, hat-shaped subgirts of various depths are roll formed by passing a sheet metal strip of uniform thickness through successive stands containing forming rolls wherein the sheet metal strip is reshaped incrementally into the desired profile. As the strip travels through the roll forming apparatus, the opposite sides of the sheet metal strip are freely drawn-in laterally to provide sheet metal for forming the overall profile and the longitudinal ribs. The free lateral draw-in of the sheet metal is desired to avoid stretching or tearing of the sheet metal, see for example COOKSON U.S. Pat. No. 3,184,942; CAMPBELL U.S. Pat. No. 3,256,566; and COOKSON U.S. Pat. No. 3,690,137.
Thus designers of building units must utilize sheet metal strips of a width sufficient to provide not only for the profile itself but also for the stiffener ribs formed in the various flat regions of the building units. Similarly, designers of individual structural elements must utilize sheet metal strips of a width sufficient for the desired profile. Since the cost of the sheet metal used to produce these components comprises a very high percentage of the total product cost, efficient utilization of the sheet metal in the design of these components is most important. Heretofore with regard to building units, a savings in the sheet metal usage could be achieved by eliminating one or more of the stiffening ribs, by reducing the depth of the decking unit, or by using a lighter gauge sheet metal. With regard to the individual structural elements, a savings in the sheet metal usage could be achieved by reducing the depth of the element or by using a lighter guage sheet. The resultant savings were balanced against the loss in strength and span capability of the building unit. More often than not, no changes were made or at most very minor changes were made.